Tetraalkyllead recovery process



Oct. 1, 1968 w. c. JAASMA TETRAALKYLLEAD RECOVERY PROCESS Filed Oct. 24.1967 United States Patent 3,403,495 TETRAALKYLLEAD RECOVERY PROCESSWilbur C. Jaasma, Greenville, S.C., assignor to Ethyl Corporation, NewYork, N.Y., a corporation of Virginia Continuation-impart of applicationSer. No. 627,014, Mar. 30, 1967. This application Oct. 24, 1967, Ser.No. 677,714

19 Claims. (Cl. 5572) ABSTRACT OF THE DISCLOSURE This invention relatesto the manufacture and recovery of tetraalkyllead compounds by a new andnovel proc ess which recovers tetraalkyllead compounds from an inert gasstream by contacting the stream at least once with an inert organicscrubbing liquid.

Cross references to related application This application is acontinuation-in-part of application Ser. No. 627,014, filed Mar. 30,1967 and now abandoned.

Background of invention The tetraalkyllead compounds, particularlytetraethyllead and tetramethyllead, are well known organometallicshighly effective as antiknock additives for hydrocarbon fuels forinternal combustion engines. These valuable chemicals may be synthesizedby many processes, one of which is the reaction of an alloy of lead andan alkali metal, especially sodium, with an alkyl halide, the alkylgroup thereof being that which is desired for attachment in thetetraalkyllead compound. As an illustration, such a reaction for thesynthesis of tetramethyllead is represented by the equation Yields inthe order of 80-90 percent are usually achieved in commercial processesutilizing the foregoing reaction.

In processes utilizing the reaction as indicated above, it is common tocarry out the process in the presence of various catalysts or catalystsystems, as well as hydrocarbon diluents, catalysts, or both, to aid inthe control and handling of the reaction and reaction products.Following the reaction, both when carried out on a batch or continuousbasis, it is necessary to recover the desired tetraalkyllead compoundfrom a reaction mass which contains the tetraalkyllead product, sodiumchloride, lead, any excess alkyl halide, catalyst and other items whichmay be present during the reaction. One of the principal ways forrecovery of tetraalkyllead product is to subject the reaction mass tosteam distillation, either with or without the presence of substantialadditional quantities of water. To effect the steam distillation, thereaction mass is transferred from a reactor to steam distillationapparatus by mechanical means such as plows or conveyers within thereactor and this transfer is assisted by blanketing the reaction masswith a gas inert to the reaction mass or the components thereof andusing the inert gas pressure to assist in the transfer of a reactionmass to the steam distillation apparatus.

During the transfer of the reaction mass with inert gas, quantities ofinert gas are vented through the steam still apparatus or other ventingmeans and this venting of inert gas causes vaporization of thetetraalkyllead product and hydrocarbon diluent, catalyst and reactionbyproducts which may accompany the product.

Past efforts to prevent the loss of the tetraalkyllead product andaccompanying hydrocarbon during transfer in such a process and othertransfers or blending operations have been ineffective primarily becauseof the presence of quantities of water vapor in the venting gas stream.Previous methods have been to pass the vented gas containing thetetraalkyllead product through a condenser system in an attempt tocondense out tetraalkyllead product and accompanying hydrocarbon, ifany; however, because of the boiling points of the tetraalkylleadproducts and hydrocarbons used, attending water vapor causes iceformation within the condenser and plugging thereof. Also, the presenceof vaporizable aluminum compounds resulting from aluminum catalysts orco-catalyst systems used tend to condense and to plug the condenseralso. This plugging makes present condenser systems ineffective andcauses the loss of valuable tetraalkyllead product by failure to recoverthe tetraalkyllead product from inert gas streams.

Summary of the invention In accordance with the present invention, thereis provided in a process for the production of tetraalkyllead productwherein tetraalkyllead containing inert gas is obtained, the improvementin the recovery of tetraalkyllead product comprising, in combination:

(a) Providing a first sump or organic scrubbing liquid,

(b) Cooling a portion of said organic scrubbing liquid from said firstsump,

(c) Contacting said tetraalkyllead containing inert gas with the cooledportion of said organic scrubbing liquid to produce a first scrubbedgaseous phase and a first contacted organic liquid phase,

((1) Returning said first contacted organic liquid phase to said firstsump, and

(e) Recovering a portion of said first su-mp as said tetraalkylleadproduct.

By the process of this invention, valuable tetraalkyllead product andaccompanying hydrocarbon, if any, may be recovered in a simple and easymanner from one or more inert gas or vent streams occurring in theproduction of tetraalkyllead product and the overall yield of productfrom commercial processes may be increased.

Brief description of the drawing The drawing is a schematic flow diagramof a process of this invention showing several sections of the processpartially in detail and in cross section.

Description of a preferred embodiment The process of this invention isapplicable to the production of tetraalkylleads in general; however, theinvention will be described in reference to the production oftetramethyllead in the presence of toluene. Referring now to thedrawing, inert gas vapor from a steam still or other product recovery orproduction means containing quantities of tetramethyllead and toluene orother volatile condensables such as aluminum compounds enters theprocess of this invention by line 10 and is fed to fume scrubber 11where it is contacted with aqueous caustic solution entering fumescrubber 11 by line 12 and line 5 to produce a scrubbed gas phaseindicated in first sump vessel 13 at 14 and an aqueous liquid phase 15.Should the quantity or quality of volatile aluminum compounds, or othermaterial, in the inert gas stream of line 10 be such that condensationthereof may cause plugging of fume scrubber 11, additional quantities ofaqueous caustic solution may be added to or blended with the enteringinert gas stream by line 9 to prevent such plugging. It is clear alsothat when the process of this invention is used for the recovery oftetraalkyllead product from an inert gas stream containing no orsubstantially no volatile aluminum compound or like material, fumescrubber 11 may be bypassed or eliminated, and the product containinginert gas fed directly to vapo space 14 without any pretreatment.

A first sump in vessel 13 containing the aqueous liquid phase 15 and afirst organic liquid 16 is maintained, and organic liquid phase 16 fromthis first sump is removed by line 17 through pump 18 and line 19 'tocooler'20 where the first organic liquid phase may be cooled to atemperature of from about l F. to about 50 F. by brine entering cooler20 by line 21 and leaving by line 22. Cooled first organic liquid phasefrom cooler 20 enters tower 30 by line 31 where it contacts scrubbed gasphase 14 from vessel 13 countercurrently. Suitable packing section 32 orother contacting meanssuch as distillation plates may be provided intower 30 to permit good contact of' the liquid and gas phases. The firstorganic liquid phase after contact returns to vessel 13 and settles tothe organic liquid phase 16 with extracted tetramethyllead and toluenecontained therein, and tetramethyllead prodnot and toluene recoveredfrom the scrubbed gas phase, along with first organic liquid are removedfrom the system as product by line 33 to pump 34 and then to processproduct recovery by line 35.

By the use of weir40 located within vessel 13, first organic liquidphase is retained within the vessel, except In operation of the processover long periods, it may be necessary or desirable to provide acontinuing or intermittent aqueous caustic wash for tower 30 to preventbuildup of deposits in the contacting section 32 or the demistingsection, if any, above the contacting section. When this is necessary ordesirable, aqueous caustic solution from line 12 may be supplied in adesired quantity by line 8 through line 6 or 7 or both.

As necessary, and generally in a volume approximating that volumeremoved to product recovery, substantially pure organic scrubbing liquidmay be added to the system from a supply not shown by line 66 to line 47and then to line 48.

In most process applications, the concentration of desirable products inthe second scrubbed gaseous phase exiting tower 30 by line 50 is reducedto a minimum and the venting gas phase either may be recovered for reuseas inert gas or vented to the atmosphere without pollution. In operationin this manner as a single tower system, it is desirable to supplysubstantially pure organic scrubbing liquid in a necessary volume tothat portion of the scrubbing liquid being pumped to cooler 20 and thismay be accomplished as shown by line 67 from supply line 66.

Under certain conditions of production and high volumes of vent gas, itis sometimes desirable to remove only a major portion of product fromthe inert gas system in tower 30 and to remove the final minorportion ofthe product in tower 51 which may be substantially identical to tower30. When operating the process of this invention in this manner, secondscrubbed gaseous phase exiting tower 30 by line 50 is fed to the bottomportion of tower 51 where it is contacted countercurrently with organicscrubbing liquid from sump 52 in the bottom portion of tower 51. Theorganic liquid is removed by line 53 and pumped by pump 54 through line55 to cooler 56 and from cooler 56 to the top portion of tower 51 byline 57. As in the case with cooler 20, chilled brine enters cooler 56by line 58 and exits by line 59 to cool the organic liquid to atemperature of from about F. to about 50 F. The second contactingorganic liquid phase flows down tower 51 to sump 52 which is connectedby line 61 to first sump'16 so that product containing organic liquiddoes not build up .within sump 52 beyond the level of connecting line 61and any excess product containing organic liquid flows to sump 16 withinvessel 13 for use in the first contacting in tower 30 and subsequentremoval to product recovery. Any aqueous phase which may be present insecond sump 52 as indicated at 60 also may flow to the first sump invessel 13 for joining with the aqueous phase therein as indicated at 15.

When the system is operated using two contacting towers, substantiallypure organic scrubbing liquid 'may be charged to the system of bothsumps; however, it is preferred to charge it by line 63 only in aquantity substantially equal to that being" removed to product recovery.In this manner, substantially pure organic contacting liquid is used toremove the remaining trace quantities of product from gaseous phaseentering tower 51 to obtain a more efficient operation. Connecting line64 joining line 48 may be provided to pump quantities of organic liquidto first sump 16 to maintain the desired level, if needed, and thesubstantially product free inert gas exiting tower 51 by line 65 may bevented to the atmosphere without air pollution problems or recovery forreuse in an inert gas system, if desired.

In operation, the absorption of the tetraalkyllead product andhydrocarbon present, if any, may be obtained in only one column;however, in treating an inert gas containing tetramethyllead andtoluene, it is preferred to use at least two absorption towers operatingin series as described above. Inert gas vapor containing vaporousproduct is fed to a fume scrubber wherein contact is made with anaqueous caustic solution, and in operation of the process for therecovery of tetramethyllead and toluene, it is preferred to use anaqueous solution of sodium hydroxide having a concentration of fromabout 1 to about 25 percent by weight of said aqueous solution. An evenmore preferred caustic concentration is from about 2 to about 8 percentby weight of said aqueous solution.

One purpose of the fume scrubber is to remove any vaporizable compoundswhich may have been formed as by-product in the tetraalkylleadproduction reaction or in other reactions. In the manufacture oftetramethyllead, organo aluminum compounds, alone or in combination withother compounds, may be used as catalysts for the production reactionand during the reaction, vaporizable organo aluminum compounds may beformed and be present in the inert gas vapor. These compounds, ifpresent, will precipitate out causing the fouling of process apparatussurfaces when an inert gas stream is treated in accordance with thisinvention to recover the tetramethyllead product. When these organoaluminum compounds are present, it is preferred to use an aqueoussolution of sodium hydroxide; however, it is clear that if othercatalyst systems or other co-catalyst systems are used, other scrubbingsystems to remove such compounds are clearly within the scope of thisinvention.

Any organic liquid having high solvency for the produced tetraalkylleadcompound may be used in the organic liquid contacting steps, and it ispreferred to use an organic liquid which may be added to or blended withthe desired tetraalkyllead product in subsequent processing steps. Whenrecovery of tetramethyllead or tetramethyllead and toluene mixtures iseffected by the process of this invention, it is preferred to use analkyl halide compound such as ethylene dichloride or ethylene dibromideas organic liquid. 1

Insert gas containing the tetraalkyllead compound to be recovered mayenter the process of this invention at substantially any pressure andany temperature. It is preferred. for simplicity of operation andconstruction of apparatus that the process of this invention be operatedat substantially atmospheric pressure, and the temperature of theproduct containing inert gas entering the process of the inventionshould be within the known limits of thermal stability of thetetraalkyllead product to be recovered. In the manufacture oftetramethyllead and its recovery in accordance with the process of thisinvention, it is preferred that the tetramethyllead ortetramethyllead-toluene containing inert gas vapors enter the process ofthis invention at a temperature of from about 80 F. to about 130 F. andpreferably at a temperature of from about 90 F. to about 120 F.

In the process of this invention when only one contacting tower is used,it will be clear that sufiicient volumes of organic scrubbing liquidcooled to temperatures below the boiling point of the tetraalkylleadproduct to be recovered may be necessary, and in the preferred embodiment wherein tetramethyllead and toluene mixtures are recovered, itis preferred that sufficient ethylene dichloride at a temperature offrom about 20 F. to about 35 F. be used to contact the gaseous phase tocause the contacted inert gas vapors leaving the single tower to have atemperature of from about 30 F. to about 60 F.

In the embodiment for the recovery of tetramethyllead and toluenemixtures using two towers in series, it is preferred that suflicientchilled ethylene dichloride be fed to the two towers to cause thegaseous phase leaving the first tower to have a temperature of fromabout 45 F. to about 55 F. and the exiting vapors from the second towerto have a temperature of from about 30 F. to about 40 F. As is clear tothose skilled in the art, suitable brine or other cooling medium in asufficient quan tity and at a sufiiciently low temperature may be fed tothe organic liquid cooling vessels to cool the organic liquid.

In a typical example of the operation of the process of this inventionfor the recovery of tetramethyllead and toluene from a nitrogen gasstream, a vapor feed composition having a concentration of 57 percentnitrogen, 40.2 percent tetramethyllead-toluene mixture and 2.8 percentwater, all percentages by weight, and having a temperature of 100-110 F,was fed to a fume scrubber where it was scrubbed with a 4 percent byweight aqueous solution of sodium hydroxide. Scrubbed vapors continuedto a first tower where they were contacted countercurrently withethylene dichloride at a temperature of approximately 35 F. in aquantity sufficient to cause the gaseous phase leaving the first towerto have a temperature of approximately 50 F.

The contacted vapors from the overhead of the first tower were fed tothe bottom of a second tower where they were contacted countercurrentlywith ethylene dichloride entering the tower at a temperature ofapproximately 32 F. Contacted vapors entered the second tower at atemperature of approximately 50 F. and exited at a temperature ofapproximately 35 F. Both towers were substantially identical andcontained 2 inch steel pall rings in a depth in the tower sufiicient toprovide approximately three theoretical distillation plates in eachtower and each tower was operated at substantially atmospheric pressure.

The concentration of the sodium hydroxide in the aqueous causticsolution was maintained at approximately 4 percent by weight by theaddition of a 25 percent by weight aqueous sodium hydroxide solution asnecessary and fresh ethylene dichloride was added to the sump of thesecond tower as necessary to compensate for the volume of ethylenedichloride-tetramethyllead-toluene mixture removed from the sump belowthe first tower.

Approximately 90 percent of the tetramethyllead-toluene mixture in thevapor feed stream was recovered in the first tower and a total ofapproximately 99 percent of the tetramethyllead-toluene mixture in theoriginal vapor feed stream was recovered in the two tower system. Basedupon total quantity of tetramethyllead produced from a reaction processnot utilizing the process of this invention, sufiicienttetramethyllead-toluene mixture was recovered using the process of thisinvention to increase the overall yield of the tetramethyllead producedapproximately 4 to 5 percent. Similar recoveries are obtained when othertetraalkyllead products are treated in accordance with the process ofthis invention.

What is claimed is:

1. In a process for the production of tetraalkyllead product whereintetraalkyllead containing inert gas is obtained, the improvement in therecovery of tetraalkyllead product comprising, in combination:

(a) providing a first sump of organic scrubbing liquid,

(b) cooling a portion of said organic scrubbing liquid from said firstsump,

(c) contacting said tetraalkyllead containing inert gas with the cooledportion of said organic scrubbing liquid to produce a first scrubbedgaseous phase and a first contacted organic liquid phase,

(d) returning said first contacted organic liquid phase to said firstsump, and

(e) recovering a portion of said first sump as said tetraalkylleadproduct.

2. The process of claim 1 further characterized by said portion of saidorganic scrubbing liquid from said first sump being cooled suflicientlyto cause said first scrubbed gaseous phase to have a temperature of fromabout 30 F. to about 60 F.

3. The process of claim 1 further characterized by the further treatmentof said first scrubbed gaseous phase comprising, in combination:

(a) providing a second sump of said organic scrubbing liquid,

(b) cooling a portion of said organic scrubbing liquid from said secondsump,

(c) contacting said first scrubbed gaseous phase with the cooled portionof said organic scrubbing liquid from said second sump to produce asecond scrubbed gaseous phase and second contacted organic liquid phase,

(d) returning said second contacted organic liquid phase to said secondsump,

(e) providing overflow means from said second sump to said first sump tocontrol the volume of liquid in said second sump, and

(f) adding suflicient substantially pure said organic scrubbing liquidto said second sump to cause sufficient liquid to flow in said overflowmeans from said second sump to said first sump to maintain the volume oforganic scrubbing liquid in said first sump substantially constant.

4. The process of claim 3 further characterized by said portion of saidorganic scrubbing liquid from said second sump being cooled sufiicientlyto cause said second scrubbed gaseous phase to have a temperature offrom about 30 F. to about 60 F.

5. The process of claim 1 further characterized by adding sufficientsubstantially pure said organic scrubbing liquid to the said process tomaintain the volume of said organic scrubbing liquid in said first sumpsubstantially constant.

6. The process of claim 5 further characterized by the addition ofsufficient substantially pure said organic scrubbing liquid being madeto said portion of said organic scrubbing liquid to be cooled.

7. In an inert gas assisted process for transferring tetraalkylleadreaction mass from a reactor system to a steam distillation system forrecovery of tetraalkyllead product wherein tetraalkyllead containinginert vent gas is obtained, the improvement in the recovery oftetraalkyllead product comprising, in combination:

(a) scrubbing said tetraalkyllead containing inert vent gas with anaqueous caustic solution to produce a scrubbed gaseous phase and aliquid phase,

(b) collecting said liquid phase in a first sump of organic scrubbingliquid to produce an aqueous liquid phase and a first organic liquidphase in said first sump,

(c) cooling a portion of said first organic liquid phase from said firstsump,

(d) contacting said scrubbed gaseous phase with the cooled portion ofsaid first organic liquid phase to produce a second scrubbed gaseousphase and a first contacted organic liquid phase,

(e) returning said first contacted organic liquid phase to said firstsump, and

(f) recovering a portion of said first organic liquid phase from saidfirst sump as said tetraalkyllead product.

8. The process of claim 7 further characterized by said tetraalkylleadproduct being tetramethyllead.

9. The process of claim 7 further characterized by said aqueous causticsolution being an aqueous solution of sodium hydroxide having aconcentration of from about 1 to about 25 percent by weight of saidaqueous solution.

10. The process of claim 7 further characterized by said inert gas beingnitrogen.

11. The process or claim 7 further characterized by said organicscrubbing liquid being ethylene dichloride.

12. The process of claim 7 further characterized by said portion of saidorganic liquid phase being cooled sufficiently to cause said secondscrubbed gaseous phase to have a temperature of from about 30 F. toabout 60 F.

13. The process of claim 7 further characterized by said first sumpbeing provided with overflow means to recover a portion of said aqueousliquid phase for recycle as said aqueous caustic solution.

14. The process of claim 7 further characterized by mixing a portion ofsaid aqueous caustic solution with said tetraalkyllead containing inertvent gas prior to said scrubbing step.

15. The process of claim 7 further characterized by contacting saidsecond scrubbed gaseous phase at least once with a portion of saidaqueous caustic solution.

16. The process of claim 7 further characterized by adding sufiicientsubstantially pure said organic scrubbing liquid to said process tomaintain the volume of said organic scrubbing liquid in said first sumpsubstantially constant.

17. The process of claim 16 further characterized by the addition ofsufficient substantially pure said organic scrubbing liquid being madeto said portion of said organic scrubbing liquid to be cooled.

18. The process of claim 7 further characterized by the furthertreatment of said second scrubbed gaseous phase comprising, incombination:

(a) providing a second sump of said organic scrubbing liquid,

(b) cooling a portion of said organic liquid phase from said secondsump,

(c) contacting said second scrubbed gaseous phase with the cooledportion of said organic liquid phase from said second sump to produce athird scrubbed gaseous phase and a second contacted organic liquidphase,

(d) returning said second contacted organic liquid phase to said secondsump,

(e) providing overflow means from said second sump to said first sump tocontrol the volume of liquid in said second sump, and

(f) adding sufficient substantially pure said organic scrubbing liquidto said second sump to cause sufficient said second contacted organicliquid phase to flow in said overflow means from said second sump tosaid first sump to maintain the volume of said first organic liquidphase in said first sump substantially constant.

19. The process of claim 18 further characterized by said portion ofsaid organic liquid phase from said second sump being cooledsufficiently to cause said third scrubbed gaseous phase to have atemperature of from about 30 F. to about F.

No references cited.

REUBEN FRIEDMAN, Primary Examiner.

C. N. HART, Assistant Examiner.

